$ { \left[\begin{array}{rrr}{1} & {0} & {-1} \\ {-2} & {1} & {-1}\end{array}\right]+\left[\begin{array}{rrr}{4} & {-2} & {1} \\ {-2} & {-1} & {-1}\end{array}\right] = {?} } $
Solution: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{1}+{4} & {0}+{-2} & {-1}+{1} \\ {-2}+{-2} & {1}+{-1} & {-1}+{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{5} & {-2} & {0} \\ {-4} & {0} & {-2}\end{array}\right]}$